Process of concentrating acid such as nitric acid by means of a drying agent.



E. COLLETT. ACID snot; AS NITRIC ACID BY MEANS OF A DRYING AGENT. APPLIUATLOH FILED NOV 11, 19x2 PROCESS OF couommnme Patented Nov. 25, 1913.

UNITED STATES PATENT OFFICE.

'EMIL vCOLLETT, OF CHRISTIANIA, NORWAY. ASSIGNOR TO NORSK HYDRO-ELEKTRISK KVAELSTOFAKTIESELSKAB, OF CHRISTIANIA, NORWAY.

PROCESS OE CONCENTRATING ACID SUCH AS NITRIC ACID BY MEANS OF A DRYING AGENT.

of concentrating acids by means of a drying agent such as sulfuric acid. It is known to effect the concentration of nitric acid by means of passing nitric acid vapors through a column in counter current with sulfuric acid. Such a process is for instance de scribed in the U.

. When the nitric acid vapors treated are Weak and the sulfuric acid previously heated, it occurs that the heat produced by the reaction" and condensation raises the sulfuric acid, to the boiling point, and in consequence thereof the drying will not'be efiicient. in order-to obtain an efi'icient drying under these circumstances large amounts of sulfuric acid have to be employed. In order to reduce the consumption of sulfuric acid the column might be subject to cooling from outside or inside by means of a cooling jacket or a cooling worm respectively. In the first event however the cooling' will not be very efiicient and in the case of a cooling-worm being employed there is a. risk that on account of leakages cooling liquid may enter into the drying'apparatus. Now according to applicantisdnvention an efficient drying and also a rational utilization of the drying agent is obtained in that the drying operation is carried out in :-:everal sections and the drying agent cooled after each section before it is passed into the next section so that it may again act as a water absorbent. As the vapors are passed in counter current with the drying agent, the vapors, containing the largest percentage of water will first pass through the drying agent which is nearly exhausted, but whose property as a water absorbenthas been restored to some extent on account at the pre' vious cooling of the same.

The process may advantageously Specification of Letters Patent.

8. Patent No. 517,098.

.drying columns 1, .2 and 3, while the Patented Nov. 25, 191 3.

Application filed November 11, 1912. Serial No. 780,822.

ried out in the manner that in the first section or sections the greatest part of the humidity and the .heat revolved by the absorption of this latter is eliminated by'means of a comparatively large amount ofdrying agent of a lower degree of concentration which circulates upon the apparatus and whose degree of concentration is maintained nearly constant. On account of .tbe dryirg agent being here employed in comparatively larger amounts injurious raises in temperature are prevented, and ifaspecial cooling of the circulating dryingagent is necessary, this may be easily efi'ected according to the present invention by inserting a suitable cooling appartus .inthe circulation system at a suitable point in this latter (outside of the drying apparatus). The gases or vapors pro-dried in this mannerarethereupon introduced into anornei apparatus where they are being treated with a smaller amount of a drying agent of a higher degree of concentration. Here the drying of the vapors or gases is thereupon carried out to the desired extent. The concentration of the drying agent which leaves this section has been only slightly reduced and it may therefore be employed for the urpose of maintaining the concentration of the circulating drying agent of -the first system constant. An amount of drying agent corresponding to the new amounts supplied is of course withdrawn from the drying apparatus.

A plant for concentrating nitric acid according to the present invention is diagrammatically illustrated in the accompanying d ra wing.

The nitric acid vapors to be dried are introduced at 4 into the lower tower 1 of the dried vapors escape at 5 from the upper towers 3 and are led into a condenser'li from which the concentrated acid is drawn off at 7 in a liquid state. Concentrated drying agent is introduced at 8 at the top of the tower 3 and flows in a somewhat diluted state from the bottom of the tower through the pipe 9, cooler 10 and pipe 11 into the second tower 2 from which it passes in a still more diluted state through the cooler 12 and pipe 13 into the tower 1.. A greater or smaller part of the cooled liquid leaving the cooler 10. l2 or 14 respectively may be forced hack be cari into the top of the :oavers 1, 2 or 3 respeconly a quite small amount of sulfuric acid will have to be subjected to concentration and this again results in a decrease in the costs of the concentration.

I claim:

1. The process of concentrating acids, such as nitric acid, which comprises passing a current of acid vapor to be concentrated against a counter current of a drying agent, withdrawing the latter from contact with the vapor at one zone of he 0! rrcnt and introducing it into the current at another zone and cooling the agent during its passage from one zone to another.

2. The process of concentrating acid, such as nitric acid, which comprises passing an ascending current of acid vapor against a counter current of a drying agent, withdrawing the latter from contact with the vaper at one zone of the current of acid vapor,-

cooling the withdrawn agent, and introducing the cooled agent into the current of acid vapor in a zone near the zone of Witl1- drawal.

3. The process of concentrating acid, such as nitric acid, which comprises passing an ascending current of acid vapor against a counter current of a drying agent, withdrawing the latter from contact with the vapor at one zone of the current of acid vapor, cooling the withdrawn agent, and introducing the cooled agent into the current of acid vapor in zones near to and distant from the zone of withdrawal.

4. The process of concentrating acids, such as nitric acid, which consists in establishing an ascending current of acid vapor, passing a-drying agent in a counter current against the acid vapor, withdrawing the drying agent from the vapor in certain zonesnf the current, cooling the withdrawn agent, and introducing the cooled agent into the current of vapor at two different zones of the current.

In testimony that I claim the foregoing my invention, I have signed my name in presence of two subscribing witnesses.

EMIL COLLETT. Witnesses: i M. N. GUTTORNESEN,

RUTH LINDSTRoM. 

